Materials for superconducting nanowires for quantum phase-slip devices

Quantum phase-slip processes in superconducting nanowires of suitably small cross-section have been proposed as the basis for a new current standard, based on physics dual to that for the Josephson voltage standard. The practical realisation of such devices presents several challenges. We consider the requirements which need to be met in constructing a nanowire quantum-phase-slip device and in particular the need to maximise R_ξ, the normal-state resistance of a length of nanowire equal to the superconducting coherence length. Titanium and niobium-silicon are promising materials for the nanowires.